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May 2004

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Subject:
From:
"Crepeau, Phil" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 14 May 2004 09:12:16 -0700
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hi,

why would you want to conformal coat the polyimide film on a flex circuit?  basically, it is a conformal coating (only better) if you know what i mean.  would you conformal coat polyimide jacketed wire...probably not. conformal coating the terminations would make some sense.  

as you found out, to get the coating to adhere, requires some mechanical scrubbing on the polyimide to increase its surface energy as brian of corsica might say.  if you insist on coating this stuff, you might want to abrade it before you assemble anything to it.

it's friday, and i'm having fun.

phil

-----Original Message-----
From: Ashok Dhawan [mailto:[log in to unmask]]
Sent: Friday, May 14, 2004 7:39 AM
To: [log in to unmask]
Subject: [TN] Flex Circuit


Dear Technetters


I am having coating adhesion problem with flex circuits. The cover plate
material is KAPTON or Poly imide. The conformal coating material used is
humiseal 2A64. The boards are cleaned, measuring less than 4 microgram Nacl
per sq in. against acceptable value of 10.6 max.

The flex circuit is dipped twice , followed by one spray. There is 15-20
bak between each dip. There is clear evidence of dewetting after first dip
and 2 dip. The spray coat is unacle to make all uniform - especially areas
which had dewetting. Fluoroscence is weak to Nil where dewetting occured.
That requires lengthly manual touch up work. Most of the dewetting is on
edges of the board.

We are interested in roughtening up the surface - Matt Finish in place of
Glossy Finish. We did scrubbed few samples and observed marked improvement
in adhesion of coating to surface.

Any one who can suggest IPC Standard, Military Standard or any other
industrial standard where this process step is specified as controlled
process ?

Our customer is Mil Standard, IPC and J-STD user and is concerned with
where Plasma etch is controlled process ?

Any help on this will be highly appreciated.

Regards

Ashok Dhawan
Solectron Winnipeg
(204) 631 7208

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